About $358 at newegg.
That's all the extra you have to pay for the 9% that the 3800 gives you. Great deal right? Well maybe not, but that's the price, that close to bleeding edge.
In straight forward terms, the 3800 is 9% faster than the 3500. It is clocked at 2.4ghz, while the 3500 is clocked at 2.2 ghz.